Herring Gulls and Great Black-Backed Gulls as Indicators of Contaminants in Bald Eagles in Lake Ontario, Canada

Abstract

In 2000, a pair of bald eagles (Haliaeetus leucocephalus) nested successfully along the shorelines of Lake Ontario in North America for the first time since 1957. However, it is a continuing question whether bald eagles will be able to reproduce successfully as they return to nest on Lake Ontario. Great black-backed gulls (Larus marinus) and herring gulls (L. argentatus) were selected as surrogate species to predict contaminant levels in eggs of bald eagles nesting on Lake Ontario. Because of the suspected overlap in the diets of great black-backed gulls and bald eagles (i.e., fish, gull chicks, and waterfowl), the two species probably occupy a similar trophic level in the Lake Ontario food web and, thus, may have similar contaminant levels. Fresh great black-backed gull and herring gull eggs were collected from three study sites in eastern Lake Ontario in 1993 and 1994 and analyzed for contaminants. Average contaminant levels of dichlorodiphenyldichloroethane (p,p'-DDE), total polychlorinated biphenyls (PCBs), and dieldrin in great black-backed gull eggs were 12.85, 26.27, and 0.27 microg/g, respectively. The mean ratio of contaminant levels in great black-backed gull eggs to contaminant levels in herring gull eggs for these three contaminants was 2.09 (range of means, 1.73-2.38). Predicted levels of contaminants in bald eagle eggs in Lake Ontario would be expected to be similar to the mean levels reported for great black-backed gull eggs. As a comparison, contaminant levels in bald eagle eggs collected from other Great Lakes nesting sites were compared to mean levels reported for herring gull eggs collected from nearby sites in 1986 to 1995. The mean ratio of contaminant levels in bald eagle eggs to contaminant levels in herring gull eggs from these sites for DDE, total PCBs, and dieldrin was 2.40 (range of means, 1.73-3.28). These ratios are very similar to those reported using great black-backed gull eggs, illustrating the apparent similarity in trophic status shared by the two top predator species at these Great Lakes sites. Predicted levels of contaminants in bald eagle eggs at Lake Ontario are similar to levels reported for bald eagles breeding at other Great Lakes sites, suggesting that bald eagles may be able to breed on the shores of Lake Ontario. However, it is unclear at this time what level of breeding success should be expected, given that productivity at other similarly contaminated Great Lakes sites may be below that required to sustain a successful breeding population. The absence of an inland bald eagle population from which bald eagles may begin to colonize the shorelines of Lake Ontario may be delaying initiation of nesting site selection; other factors such as habitat and prey availability would likely not limit reproductive success.

Further declines in organochlorines in eggs of red-breasted mergansers from Lake Michigan, 1977–1978 versus 1990 versus 2002

“…In 1975, White and Cromartie (1977) analyzed 18 red-breasted merganser eggs from the same area in Lake Michigan as we collected from; the mean concentration of PCBs was 45 μg/g, compared to 21 μg/g in our 1977-1978 collection, 8.5 μg/g in our 1990 collection, and 4.6 μg/g in our 2002 collection. The White and Cromartie (1977) means were arithmetic means, but according to White (personal communication) the arithmetic and geometric means were very Table 1 Comparison of organochlorine pesticides and PCBs (μg/g, wet-weight; n = 12) in red-breasted merganser eggs collected in 1977-1978, 1990, and 2002from Lake Michigan 1977-197819902002 PCBs 21 a (10-34) b A 8.5 (4.0-14) B 4.6 (1.8-13) C p, p -DDE 6.5 (3.3-11) A 2. 2 (1.1-3.3 Faber and Hickey (1973), and the 1975 data came from White and Cromartie (1977) sites, dieldrin declined from 1.0 μg/g in 1975 to 0.82 μg/g in 1977-1978, 0.69 μg/g in 1990, and 0.03 μg/g in 2002, suggesting that, following a steady but slow decline in the 1970s and 1980s, a more rapid decline took place in the 1990s.…”

“…Contaminants were suspected as the cause of impaired reproduction of bald eagles (Haliaeetus leucocephalus) in Lake Superior (Kozie and Anderson 1991), Forster's terns (Sterna forsteri) from Lake Michigan (Kubiak et al 1989), and double-crested cormorants from Lake Michigan and other Great Lakes (Tillitt et al 1992). Weseloh et al (2002) concluded that DDE, PCBs, and possibly mirex, at levels estimated to be in bald eagle eggs in 1993 and 1994 in certain parts of the Great Lakes, might still be having an adverse impact on productivity. Continued monitoring of contaminant burdens and reproductive success is still needed for the more sensitive species of fish-eating birds.…”

Estimating the relative use of anthropogenic resources by Herring Gull (Larus argentatus) in the Bay of Fundy, Canada

“…Generally, migratory birds are of conservation interest because of the essential roles they play in ecosystems, their cultural appeal and symbolic importance, and because population declines have been observed on local to global scales (Cury et al 2011, Rosenberg et al 2019. Avian species have additionally served as indicators of ecosystem health in conservation and restoration projects worldwide (Weseloh et al 2002, Frederick et al 2009, Scopel et al 2018, Velarde et al 2019. Despite these values, gulls (Larus spp.)…”

Regression models for explaining and predicting concentrations of organochlorine pesticides in fish from streams in the United States

“…They also induce the monooxygenase enzymes [13] and have been associated with fish diseases [14], endocrine and reproductive changes [15], and immunosuppressive effects [16]. Despite nationally declining trends, there is potential for remaining organochlorine residues to adversely affect aquatic life and wildlife, especially given the uncertainty in thresholds for adverse effects [17,18]. Organochlorine pesticides were widely detected in fish and sediment from U.S. streams during the 1990s, and concentrations in some areas were high compared with environmental benchmarks [2] ( Supporting Information Table S1; ).…”